1. Field of the Invention
The present invention relates to a scroll hydraulic machine used as a compressor or an expansion device. The present application is based on Japanese Patent Application No. 9-23101, the contents of which are herein incorporated by reference.
2. Description of the Related Art
To a hydraulic machine having a fixed scroll and a swirling scroll engaging with the fixed scroll and performing a swirling motion, there is mounted a balance weight for balancing a dynamic imbalance due to a revolutionary swirling motion of the swirling scroll.
FIG. 4 is a front elevational view of a conventional balance weight 27 and a cross sectional view along a line B--B in FIG. 4 as shown in FIG. 5. The balance weight 27 has a semicircular plate shape and is mounted to an outer periphery of a drive bush 21 rotating integrally with a rotating shaft (not shown).
In the conventional scroll hydraulic machine mentioned above, a centrifugal force acted on the swirling scroll and the balance weight is expressed by the following equation: EQU Centrifugal force=(M.sub.O -M.sub.B).multidot..rho..multidot..omega..sup.2
in which M.sub.O is a mass of the swirling scroll, M.sub.B is a mass of the balance weight, .rho. is a radius of a revolutionary swirling of the swirling scroll and .omega. is a rotational angular velocity of the swirling scroll.
Since the centrifugal force is small when the swirling scroll is rotating at a low speed, a force for bringing a spiral wrap of the swirling scroll into contact with a spiral wrap of the fixed scroll becomes small, so that there has been a problem in an amount of gas leaking from an inner portion of a compression chamber.
Further, since the centrifugal force becomes large when the swirling scroll is rotating at a high speed, a force for bringing the spiral wrap of the swirling scroll into contact with the spiral wrap of the fixed scroll becomes excessive, so that there has been a risk that these spiral wraps would be broken.